1. Field of the Invention
The present invention relates generally to reversing flow regenerative incinerator systems for waste gases containing volatile hydrocarbon compounds, and more particularly, to purging and treating entrapped gas during flow reversal periods, in order to ensure attaining and maintaining high incinerator system destruction efficiency.
2. Description of the Prior Art
Regenerative incinerator systems use gas flow reversal to recapture heat which would otherwise be lost to the atmosphere. Regenerative incinerator systems consist minimally of a gas heating regenerator which receives the gas, a burner to oxidize the gas and a regenerator which cools the gas reclaiming some of the heat of the combustion process. After a period of time the flow of gas through the system is reversed. The exhaust regenerator now becomes the heating regenerator and the former gas heating regenerator now becomes the cooling regenerator through which the gas passes prior to being released to the atmosphere.
A problem exists with this system during flow reversal. The intake regenerator contains unburned gases which would be released if not purged prior to flow reversal. Current regenerative incinerator systems use positive pressure within the intake regenerator to purge these gases prior to flow reversal. Incinerated air is introduced into the regenerator which forces the residual gas up through a media bed and into the combustion chamber. This leaves incinerated air in the regenerator to be exhausted when the gas flow is reversed. The introduction of this incinerated air causes the system (exhaust fan) to handle this recycled air a second time. This requires a larger induced draft fan and requires burning of the recycled incinerated air, thus increasing fuel usage. This mandates a design requirement for larger processing systems with accordingly increased costs of construction and operation.
The present invention uses negative pressure, rather than positive pressure to purge the intake regenerator. The residual gas within the intake regenerator is removed by suction from the combustion air fan prior to flow reversal. The present invention removes by negative pressure the air from the intake regenerator and voids in the ceramic media, utilizing the combustion fan and then sends it to the combustion burners. Any excess over and above with the combustion burners require will be returned to the inlet. This reduces the need for fuel and/or outside combustion air, depending on the composition of the purged air. The system need not be oversized, as with current systems, due to the lower volume of purging air needed and its efficient use. The result is a significant savings in construction and operation.
The present system may also employ a separate fan to purge the third idle vessel and return the purge air back to the inlet of the regenerative system, rather than using the combustion blower for purging. A combination of blowers may also be used in moving the purged air to the combustion burners. One blower can be used for high pressure combustion air for preheat of the ceramic media and one blower can be used for low pressure for continuous operation after pre-heat. The existing system uses positive pressure within the intake regenerator to force the heavier-than air solvents in the contaminated gas up into the combustion chamber. This works against gravity. The current invention cooperates with the settling effect of gravity on the heaver entrapped solvents in the process system, by placing its purging inlet at the bottom of the regenerator. The efficiency of removal is increased and therefore, heavy solvents in the gas remaining in the inlet regenerator is reduced. This will reduce the amount of purge required and will insure more complete removal of the solvents. This provides for a higher destruction efficiency of the regenerative incineration system.
The invention, as does the prior art, utilizes dampers to control the flow of gas and contaminated air through the system. All dampers have some leakage. Such leakage allows small amounts of untreated gas and air to be exhausted into the atmosphere. One embodiment of the invention utilizes valves at critical locations consisting of single dampers with double blades with a fresh air source between them. Leakage of such single dampers with double dampers results in the movement of atmosphere air rather than gas or contaminated air into the atmosphere.
The prior art typically removed 95%-98% of the hydrocarbons from the treated gas as determined from measured inlet and outlet hydrocarbon concentrations. The result of all of the above improvements provided by the present invention is the removal of 98%-99% of hydrocarbons from the processed gas and reduced combustion fuel usage.